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uniform sampler2D u_ScreenDepthMap;
uniform vec4 u_ViewInfo; // zfar / znear, zfar
varying vec2 var_ScreenTex;
vec2 poissonDisc[9] = vec2[9](
vec2(-0.7055767, 0.196515), vec2(0.3524343, -0.7791386),
vec2(0.2391056, 0.9189604), vec2(-0.07580382, -0.09224417),
vec2(0.5784913, -0.002528916), vec2(0.192888, 0.4064181),
vec2(-0.6335801, -0.5247476), vec2(-0.5579782, 0.7491854),
vec2(0.7320465, 0.6317794)
);
// Input: It uses texture coords as the random number seed.
// Output: Random number: [0,1), that is between 0.0 and 0.999999... inclusive.
// Author: Michael Pohoreski
// Copyright: Copyleft 2012 :-)
// Source: http://stackoverflow.com/questions/5149544/can-i-generate-a-random-number-inside-a-pixel-shader
float random( const vec2 p )
{
// We need irrationals for pseudo randomness.
// Most (all?) known transcendental numbers will (generally) work.
const vec2 r = vec2(
23.1406926327792690, // e^pi (Gelfond's constant)
2.6651441426902251); // 2^sqrt(2) (Gelfond-Schneider constant)
//return fract( cos( mod( 123456789., 1e-7 + 256. * dot(p,r) ) ) );
return mod( 123456789., 1e-7 + 256. * dot(p,r) );
}
mat2 randomRotation( const vec2 p )
{
float r = random(p);
float sinr = sin(r);
float cosr = cos(r);
return mat2(cosr, sinr, -sinr, cosr);
}
float getLinearDepth(sampler2D depthMap, const vec2 tex, const float zFarDivZNear)
{
float sampleZDivW = texture2D(depthMap, tex).r;
return 1.0 / mix(zFarDivZNear, 1.0, sampleZDivW);
}
float ambientOcclusion(sampler2D depthMap, const vec2 tex, const float zFarDivZNear, const float zFar)
{
float result = 0;
float sampleZ = zFar * getLinearDepth(depthMap, tex, zFarDivZNear);
vec2 expectedSlope = vec2(dFdx(sampleZ), dFdy(sampleZ)) / vec2(dFdx(tex.x), dFdy(tex.y));
if (length(expectedSlope) > 5000.0)
return 1.0;
vec2 offsetScale = vec2(3.0 / sampleZ);
mat2 rmat = randomRotation(tex);
int i;
for (i = 0; i < 3; i++)
{
vec2 offset = rmat * poissonDisc[i] * offsetScale;
float sampleZ2 = zFar * getLinearDepth(depthMap, tex + offset, zFarDivZNear);
if (abs(sampleZ - sampleZ2) > 20.0)
result += 1.0;
else
{
float expectedZ = sampleZ + dot(expectedSlope, offset);
result += step(expectedZ - 1.0, sampleZ2);
}
}
result *= 0.33333;
return result;
}
void main()
{
float result = ambientOcclusion(u_ScreenDepthMap, var_ScreenTex, u_ViewInfo.x, u_ViewInfo.y);
gl_FragColor = vec4(vec3(result), 1.0);
}
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